Radishes are relatives to the cabbage family. There are enzymes that cause a reaction and the production of a mustard oil which is what gives the radish it's pungency. The enzyme is in highest concentration in the skin. Like cabbage radishes have sulphur compounds which I assume is what you are smelling. Soaking in water may help to reduce these compounds. Chopping will increase them and acidifying is known to increase them as well.

Do you recall how you cooked it? I just peel it, cut it into rounds and simmer them for bit. I use plain water if using it in Japanese style soups, or a stronger soy sauce flavored liquid if serving it on its own (or with mushrooms). I also add it to Chinese style beef stews. I've never noticed a strong odor.